This re-lands r15776 and r15777, reverting the revert in r15786.

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/22144006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16071 ce2b1a6d-e550-0410-aec6-3dcde31c8c00